Electric consommation and solar panel

[Maiki]

Hi everybody,
I have a little fridge (14L) in my Pajero. Actually I have 2 batteries in my car.
But when I stay a long time (more than a day) in the same place the 2nd battery is empty.
So I'm thinking buying a solar panel. After inspect my fridge I saw it consumes 46W.
I think it's a lot for this size.

So I want to know if someone knows if it's per day or per hour?
That means I need a solar panel of 50W at least ?

A picture of the technical details on my fridge is attached.

Thanks for your return.

[conquistador]

4amps would translate to 96amp hours for 24hours. Thats huge! so I presume this with a fridge that is constantly running. Its unlikely a fridge compressor would run for a little over a third of the time so about 36ah over a 24hour period.

A 50w (divided by 12volts) solar panel will generate about 32amp hours in ideal conditions assuming 8hours of sunlight.

All depends on that fridges duty cycle.......and your battery.

[dhula]

Assuming it's this one -- Click here Having had one it stays running all the time until you either switch it off or disconnect it which explains the drained battery after a day/night

[geopaj]

Sorry but the problem is you have a 'cooler/warmer', not a fridge (as stated on the label you posted).

These are ok and have their place but 'cooler/warmers' but they operate differently to compressor fridges.

The main differences are the 'cooler/warmers' are much more power hungry and they also don't have the same cooling capacity (ie only 20-30 degrees below ambient, whereas fridges are often 50+ degrees below ambient - this can be a major issue for a unit running in a vehicle during an Australian summer where it can easily get to 50+ degrees inside if parked in the sun).

'Cooler/warmers' are best used with the engine running (due to their power use). How much will extra batteries and a solar setup cost? If you want to keep food safety (cold) for a day or more I would use an esky or put the money towards saving for a compressor fridge.

Sorry... I'm sure this is not what you wanted to hear mate.

EDIT:

4amps would translate to 96amp hours for 24hours. Thats huge!...

...A 50w (divided by 12volts) solar panel will generate about 32amp hours in ideal conditions assuming 8hours of sunlight.

Based on the above, and the generally considered max of 50% discharge, you will require a battery bank deep cycle batteries with of min 200amh (ie 2 X 100amh deep cycle batteries) for 24 hours.

If you need any more than 24 hours you will need some way of charging - so a solar setup that is capable of delivering 100amps MINIMUM per day (ie in the 5-8 hours of usable sunlight). Using Redarc's suggestion that "An 80W solar panel can realistically supply between 4 and 5 Amps on a sunny day, for most of the sunlight hours of the day. If we assume that only 1/3 of the day is sunlight hours then it is safe to assume that the panel can supply between 4 and 5 Amps for this period." (https://www.redarc.com.au/solar-faqs). Therefore an 80w panel will provide approximately 20-40amh pr day - meaning that you would require 3-5 x 80w solar panels to keep you battery bank charged.

[erad]

"A 50w (divided by 12volts) solar panel will generate about 32amp hours in ideal conditions assuming 8hours of sunlight."

This assumes that the solar panel is directly facing the sun all the time. Normally not so. I would work on 5 hours equivalent, so I would expect 50 watts (about 4 amps) times 5 equals 20 amp-hour storage. Either way, it is not enough to run a continuous 4 amp load all day. It would help, but not be enough.

[Maiki]

Thanks everybody for your return.
Geopaj it's true it's a cooler/warmer not a true fridge.
I choose it because it's smaller than a fridge and I don't have more place in my car.
It's true with a fridge I don't need 2 big batteries and 3 solar panels.

Now I understand more how it works.
So I think I'll buy a 80W solar panel. Like this during the day I don't lose power.
And turn on the engine for finishing charging the battery.

So I have an other question.
My deep cycle battery is 75A. Do you have an idea how long I need for charging it with the alternator without moving ?

Thanks again for your return.

[dhula]

I think if you wanted to charge you battery over and above what the solar panel might be able to supply, then it might be worth looking into a portable generator.
You can get a small 2 smoke generator from SCA for $200.

[conquistador]

"A 50w (divided by 12volts) solar panel will generate about 32amp hours in ideal conditions assuming 8hours of sunlight."

This assumes that the solar panel is directly facing the sun all the time. Normally not so. I would work on 5 hours equivalent, so I would expect 50 watts (about 4 amps) times 5 equals 20 amp-hour storage. Either way, it is not enough to run a continuous 4 amp load all day. It would help, but not be enough.

I did say ideal, but your right unless your chasing the sun with incessantly shifting the panel to track the sun it would be less

What i have trouble with understanding is that solar panels will generate at 17v+ and a regulator will step it down to 13-14v so as to not kill the battery. If ohms law holds does this then mean the volts turn into extra amps,watts, heat or dissapear into a parallel dimension.... just like my retention of high school electical principles?

[jimsutt]

I hate to pour cold water on your fridge etc but those electronic coolers/heaters are toys and not suitable for camping and 4wd touring. You would need a huge solar panel to keep your battery charged. During winter you are lucky to get 6 hrs a day of decent sunlight.. You would be far better off to buy a small compressor fridge you will get far greater time out of your battery and smaller solar panel. Also note that solar regulators in general are not effecient you need MPPT type for max effeciency. Hope this is helpful.

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